Similar to @Cataurus !! bind handler with picker !!

private async void Button_Click_Choose_Left_Folder(object sender, RoutedEventArgs e)
{
var folderPicker = new FolderPicker();

// 获取当前窗口的句柄（在 WinUI 或桌面应用中）
IntPtr hwnd = System.Diagnostics.Process.GetCurrentProcess().MainWindowHandle;

// 将文件夹选择器与窗口句柄关联
WinRT.Interop.InitializeWithWindow.Initialize(folderPicker, hwnd);

folderPicker.SuggestedStartLocation = PickerLocationId.PicturesLibrary;
...

var folder = await folderPicker.PickSingleFolderAsync();
}